Coil component, its manufacturing method, and circuit substrate provided with the coil component

ABSTRACT

Disclosed herein is a coil component that includes a drum-shaped core having a flange portion and a winding core around which a wire is wound. The flange portion includes first and second side surface opposite to each other, and a mounting surface. The mounting surface of the flange portion includes first and second convex portions and a concave portion positioned therebetween. The first convex portion has a third side surface parallel to the first side surface of the flange portion. The second convex portion has a fourth side surface parallel to the second side surface of the flange portion. A level difference between the first side surface and the third side surface is larger than a level difference between the second side surface and the fourth side surface.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a coil component and its manufacturingmethod and, more particularly, to a coil component using a drum-shapedcore and its manufacturing method. The present invention further relatesto a circuit substrate and, more particularly, to a circuit substrateprovided with the coil component using the drum-shaped core.

Description of Related Art

In recent years, electronic components used in an information terminaldevice such as a smartphone is strongly required to be reduced in sizeand height. Under such circumstances, a large number of surface mountcoil components such as a pulse transformer using a drum-shaped core,not a toroidal-shaped core are used. For example, Japanese PatentApplication Laid-Open No. 2014-199906 discloses a surface mount pulsetransformer using the drum-shaped core.

In the drum-shaped core of the pulse transformer described in JapanesePatent Application Laid-Open No. 2014-199906, a mounting surface of aflange portion of the core has a concavo-convex shape, and a wire endportion is connected to a convex portion (see FIG. 2 of Japanese PatentApplication Laid-Open No. 2014-199906). Each flange portion has fourconvex portions, and side surfaces of the four convex portionspositioned at both ends of the core coincide with side surfaces of theflange portions.

However, when a plurality of pulse transformers described in JapanesePatent Application Laid-Open No. 2014-199906 are mounted on a circuitsubstrate in proximity, a distance between the adjacent pulsetransformers is too small, which may deteriorate reliability. Inparticular, when a part of the terminal electrode is formed also on theside surface of each convex portion, a solder fillet is formed on theside surface of each convex portion, with the result that the aboveproblem becomes more prominent.

The above problem is not a problem that occurs only in the pulsetransformer, but a problem occurs commonly in coil components using thedrum-shaped core.

SUMMARY

An object of the present invention is therefore to provide a coilcomponent capable of ensuring reliability even when a plurality of thecoil components are mounted on a circuit substrate in proximity and amanufacturing method for the coil component.

Another object of the present invention is to provide a circuitsubstrate on which such coil components are mounted.

A coil component according to the present invention includes: adrum-shaped core having a pair of flange portions and a winding corepositioned between the pair of flange portions; a plurality of terminalelectrodes formed in each of the flange portions; and plurality of wireswound around the winding core and having a plurality of end portionsconnected to their corresponding terminal electrodes. The flange portionhas a mounting surface parallel to an axial direction of the windingcore and first and second side surfaces parallel to the axial directionof the winding core and to each other. The mounting surface has aplurality of convex portions and a concave portion positioned betweenthe plurality of convex portions. The terminal electrodes are eachformed at least on the convex portion, and thus the terminal electrodesformed on the mounting surface are isolated by the concave portion. Outof the plurality of convex portions, a first convex portion closest tothe first side surface is parallel to the first side surface and has athird side surface positioned at the first side surface side. Out of theplurality of convex portions, a second convex portion closest to thesecond side surface is parallel to the second side surface and has afourth side surface positioned at the second side surface side. A leveldifference between the first side surface and the third side surface islarger than a level difference between the second side surface and thefourth side surface.

A circuit substrate according to the present invention includes asubstrate having a plurality of land patterns, the above-described coilcomponent mounted on the circuit substrate, and a solder connecting theplurality of land patterns and the plurality of terminal electrodes.

According to the present invention, a level difference is formed at theside surface of the flange portion, making it difficult for a terminalelectrode of one coil component to be short-circuited to a terminalelectrode of another coil component. This can increase reliability of aproduct. For example, even in a case where two coil components aremounted on the substrate such that the first side surface of one coilcomponent and the second side surface of the other coil component faceeach other, a sufficient distance can be ensured between both theterminal electrodes. In addition, a level difference between the secondside surface and the fourth side surface is relatively small, so that asize of the coil component is not increased more than necessary.

In the present invention, preferably the terminal electrode is furtherformed at the third and fourth side surfaces. In this case, a solderfillet is formed at the third and fourth side surfaces, theabove-described short circuit is likely to occur; however, highreliability can be ensured even in this case.

In the present invention, preferably the second side surface and thefourth side surface form the same plane. This can reduce a size of thecoil component.

In the present invention, preferably the drum-shaped core has a two-foldrotation-symmetrical shape. With this configuration, the coil componenthas no directivity, thus facilitating mounting work.

In the present invention, it is preferable that the plurality of convexportions further includes third and fourth convex portions, that thefirst, third, fourth, and second convex portions are arranged in thisorder, and that the plurality of terminal electrodes include first,second, third, and fourth electrodes formed respectively on the first,second, third, and fourth convex portions. With this configuration, thecoil component can be used as a pulse transformer.

In this case, preferably a gap between the third and fourth convexportions is larger than a gap between the first and third convexportions and a gap between the second and four convex portions. This canincrease a breakdown voltage between primary and secondary sides. Whenthe second and fourth terminal electrodes are used as a center tap, acommon land pattern may be provided on the substrate for the second andfourth terminal electrodes. In this case, more preferably the second andfourth terminal electrodes are short-circuited via a bridge of thesolder. This allows reliable short circuit of the center tap.

Further, in this case, preferably the gap between the first and thirdconvex portions and the gap between the second and fourth convexportions differ from each other. This facilitates the short circuit ofthe center tap.

The first, second, third, and fourth terminal electrodes are preferablyformed on side surfaces of the respective first, second, third, andfourth convex portions. Assuming that the gap between the first andthird convex portions or the gap between the second and fourth convexportions is a, and a height of each of the first, second, third, andfourth terminal electrodes formed on the side surfaces of respectivefirst, second, third, and fourth convex portions is b,

b/a≧⅓ is preferably satisfied. Satisfying this condition facilitatesformation of the solder bridge.

A coil component manufacturing method include a first process ofpreparing a drum-shaped core having a pair of flange portions and awinding core positioned between the pair of flange portions, a secondprocess of forming a plurality of terminal electrodes on each of theflange portions, and a third process of winding a plurality of wiresaround the winding core and connecting end portions of the wire to theircorresponding terminal electrodes. The flange portion has a mountingsurface parallel to an axial direction of the winding core and first andsecond side surfaces parallel to the axial direction of the winding coreand to each other. The mounting surface has a plurality of convexportions and a concave portion positioned between the plurality ofconvex portions. Out of the plurality of convex portions, a first convexportion closest to the first side surface is parallel to the first sidesurface and has a third side surface positioned at the first sidesurface side. Out of the plurality of convex portions, a second convexportion closest to the second side surface is parallel to the secondside surface and has a fourth side surface positioned at the second sidesurface side. A level difference between the first side surface and thethird side surface is larger than a level difference between the secondside surface and the fourth side surface. The second process prepares anelectrode material in a liquid or paste form and dips the convexportions in the electrode material such that the concave portions is notbrought into contact with the electrode material.

With the above procedure, the terminal electrode can be easily formed onthe convex portion.

As described above, according to the present invention, there can beprovided a coil component capable of ensuring reliability even when aplurality of the coil components are mounted on a substrate in proximityand a manufacturing method for the coil component. Further, there can beprovided a circuit substrate on which such coil components are mounted.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention will be moreapparent from the following description of certain preferred embodimentstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic perspective view illustrating an externalappearance of a coil component according to a first embodiment of thepresent invention;

FIG. 2 is a plan view illustrating a conductor pattern on the circuitsubstrate on which the coil component shown in FIG. 1 is mounted;

FIG. 3 is a circuit diagram of a LAN connector circuit (100 Base);

FIG. 4 is a circuit diagram of a LAN connector circuit (1000 Base);

FIG. 5 is a schematic diagram for explaining a method for formingterminal electrodes;

FIG. 6 is a schematic perspective view illustrating an externalappearance of a coil component according to a modification of the firstembodiment;

FIG. 7 is a schematic perspective view illustrating an externalappearance of a coil component according to a second embodiment of thepresent invention;

FIG. 8 is a plan view illustrating a conductor pattern on the circuitsubstrate on which the coil component shown in FIG. 7 is mounted;

FIG. 9 is a schematic perspective view illustrating an externalappearance of a coil component according to a first modification of thesecond embodiment;

FIG. 10 is a schematic perspective view illustrating an externalappearance of a coil component according to a second modification of thesecond embodiment;

FIG. 11 is a schematic perspective view illustrating an externalappearance of a coil component according to a third modification of thesecond embodiment;

FIG. 12 is a schematic perspective view illustrating an externalappearance of a coil component according to a third embodiment of thepresent invention;

FIG. 13 is a plan view illustrating an example of a conductor pattern onthe circuit substrate on which the coil component shown in FIG. 12 ismounted;

FIG. 14 is a plan view illustrating another example of a conductorpattern on the circuit substrate on which the coil component shown inFIG. 12 is mounted;

FIG. 15 is a side view of the coil component shown in FIG. 12 mounted onthe circuit substrate;

FIG. 16 is a side view of a modified coil component of the coilcomponent shown in FIG. 12 mounted on the circuit substrate; and

FIG. 17 is a side view of the modified coil component mounted on thecircuit substrate in which a width of a land pattern is enlarged.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will be explained belowin detail with reference to the accompanying drawings.

FIG. 1 is a schematic perspective view illustrating an externalappearance of a coil component 10A according to a first embodiment ofthe present invention.

The coil component 10A according to the present embodiment is a surfacemount coil component and includes, as illustrated in FIG. 1, adrum-shaped core 20A, a plate-like core 30 bonded to the drum-shapedcore 20A, and two wires W11 and W12 wound around a winding core 21 ofthe drum-shaped core 20A. Use of the coil component 10A according to thepresent embodiment is not especially limited, and the coil component 10Amay be used as a filter such as a common mode choke coil or as atransformer.

Each of the drum-shaped core 20A and the plate-like core 30 is formed ofa magnetic material having a comparatively high permeability, such as anNi—Zn ferrite sintered body or an Mn—Zn ferrite sintered body. Themagnetic material having a high permeability, such as the Mn—Zn ferrite,generally has a low specific resistance and thus has conductivity.

The drum-shaped core 20A has a rod-like winding core 21 and a pair offlange portions 22A and 23A provided at axial direction (y-direction)both ends of the winding core 21. The winding core 21 and flangeportions 22A and 23A are integrally formed. The flange portions 22A and23A each have an inner surface Si connected to the winding core 21 andan outer surface So positioned at an opposite side to the inner surfaceSi. The inner surface Si and the outer surface So constitute an xzplane. The flange portions 22A and 23A further has a mounting surfaceSb, a bonding surface St, a first side surface S1 and a second sidesurface S2. The mounting surface Sb and the bonding surface St extend inparallel and constitute an xy plane and. The first and second sidesurfaces S1 and S2 extend in parallel and constitute a yz plane.

The coil component 10A is a component that is surface-mounted on aprinted circuit board in actual use with the mounting surface Sb of theflange portions 22A and 23A facing the printed circuit board. Theplate-like core 30 is secured by adhesive to the bonding surfaces St ofthe respective flange portions 22A and 23A. With this configuration, aclosed magnetic path is formed by the drum-shaped core 20A and theplate-like core 30.

As illustrated in FIG. 1, the mounting surface Sb of each of the flangeportions 22A and 23A has a concavo-convex shape. More specifically, eachof the flange portions 22A and 23A has two convex portions on themounting surface Sb, and the two convex portions are separated by aconcave portion. Terminal electrodes are formed respectively on topsurfaces of the convex portions. Specifically, the flange portion 22Ahas two terminal electrodes E11 and E12, and the flange portion 23A hastwo terminal electrodes E13 and E14. The terminal electrodes E11 to E14are formed by conductive films coated on the corresponding flangeportions 22A and 23A. The conductive film is not coated on the concaveportion. Thus, the plurality of terminal electrodes (e.g., E11 and E12)formed in the same flange portion are electrically isolated from eachother by the concave portion having no conductive film.

As illustrated in FIG. 1, two wires W11 and W12 are wound around thewinding core 21. One ends of the respective wires W11 and W12 areconnected respectively to the terminal electrodes E11 and E12, and theother ends thereof are connected respectively to the terminal electrodesE14 and E13. The connection of the wires W11 and W12 is made on theconvex portions of the mounting surface Sb. A method for the wireconnection is not especially limited. For example, the wire connectioncan be made by thermo-compression bonding or laser bonding.

The terminal electrodes E11 to E14 are each formed not only on the topsurface of the convex portion, but also on apart of each of sidesurfaces constituting the convex portion. That is, each convex portionhas a side surface positioned at the inner surface Si side, a sidesurface positioned at the outer surface So side, a side surfacepositioned at the first side surface S1 side, and a side surfacepositioned at the second side surface S2 side, and a part of each of theterminal electrodes E11 to E14 is formed at upper portions of the abovefour side surfaces. The reason that the terminal electrodes E11 to E14each have such a shape is due to a formation method for the terminalelectrode to be described later.

Out of the four side surfaces constituting the convex portioncorresponding to the terminal electrode E11, a side surface positionedat the first side surface S1 is assumed to be a third side surface S3.In this case, the first and third side surfaces S1 and S3 are parallelto each other, and a level difference therebetween is L1. On the otherhand, out of the four side surfaces constituting the convex portioncorresponding to the terminal electrode E12, a side surface positionedat the second side surface S2 is assumed to be a fourth side surface S4.In this case, the second and fourth side surfaces S2 and S4 form thesame plane. That is, the second and fourth side surfaces S2 and S4 areparallel to each other, and a level difference L2 therebetween is zero(L1>L2).

The convex portions corresponding to the terminal electrodes E13 and E14have shapes rotation symmetrical (two-fold rotation symmetrical)respectively to the convex portions corresponding to the terminalelectrodes E11 and E12. Thus, assuming that, out of the four sidesurfaces constituting the convex portion corresponding to the terminalelectrode E13, a side surface positioned at the first side surface S1 isassumed to be a third side surface S3, the first and third side surfacesS1 and S3 are parallel to each other, and a level differencetherebetween is L1. On the other hand, assuming that, out of the fourside surfaces constituting the convex portion corresponding to theterminal electrode E14, a side surface positioned at the second sidesurface S2 is assumed to be a fourth side surface S4, the second andfourth side surfaces S2 and S4 form the same plane. That is, the secondand fourth side surfaces S2 and S4 are parallel to each other, and alevel difference L2 therebetween is zero (L1>L2).

The drum-shaped core 20A need not be rotation symmetrical; however, whenit is rotation symmetrical, the coil component 10A has no directivity,thus facilitating mounting work.

Surfaces of each of the flange portions 22A and 23A other than the topsurface thereof do not have the concavo-convex shape. In particular, thebonding surface St has substantially a flat shape and thus comes intoclose contact with the flat plate-like core 30.

This is a structure of the coil component 10A according to the firstembodiment of the present invention.

FIG. 2 is a plan view illustrating a conductor pattern on the circuitsubstrate on which the coil component 10A is mounted.

In the example of FIG. 2, two mounting regions 31 and 32 are allocatedon the substrate, and the coil components 10A are mounted respectivelyin the mounting regions 31 and 32. The mounting regions 31 and 32 arelaid out in proximity with each other in an x-direction so as to realizehigh density mounting on the circuit substrate. Specifically, a gapbetween the mounting regions 31 and 32 is L0. A minimum value of the gapL0 is controlled depending on required reliability, specification,required mounting accuracy, and the like.

In a case where the coil component 10A according to the presentembodiment is a common mode choke coil, such a layout is required in,e.g., a LAN connector circuit (100 Base) illustrated in FIG. 3 and a LANconnector circuit (1000 Base) illustrated in FIG. 4. As illustrated inFIGS. 3 and 4, a plurality of common mode choke coils CM are used in theLAN connector, so that the mounting regions 31 and 32 may be inproximity when high density mounting is applied.

In each of the mounting regions 31 and 32, land patterns P11 to P14connected respectively with the terminal electrodes E11 to E14 areprovided. The terminal electrodes E11 to E14 and land patterns P11 toP14 are electrically and mechanically connected to each other,respectively, by soldering.

In the present embodiment, the convex portion corresponding to theterminal electrode E11 has the level difference L1, so that anx-direction gap between the land patterns P11 and P12 of the differentcoil components 10A is increased to a value obtained by L0+L1.Similarly, the convex portion corresponding to the terminal electrodeE13 has the level difference L1, so that an x-direction gap between theland patterns P13 and P14 of the different coil components 10A isincreased to a value obtained by L0+L1. That is, even when the gap L0 isvery small, the land gap between the different coil components 10A cansufficiently be ensured.

To ensure the land gap is more important in a case where a size of eachof the land patterns P11 to P14 is larger than a size of each of theterminal electrodes E11 to E14. This is because, as illustrated in FIG.1, when a part of the terminal electrode is formed also on the sidesurfaces of the convex portion, a solder fillet may be formed when thesize of each of the land patterns P11 to P14 is large, so that when thegap L0 is too small, a short circuit failure is likely to occur.However, the level difference L1 is added in the present embodiment, sothat the short circuit failure can be prevented in such a case.

In order to prevent the above short circuit failure, it can beconsidered that the level difference L2 is set not to zero, but to avalue equivalent to the level difference L1. That is, L2 may be setequal to L1. However, in this case, a size of the coil component 10A inthe x-direction is increased. In view of this point, in the presentembodiment, the level difference L1 is set large, while the leveldifference L2 is set small (zero), whereby both prevention of the shortcircuit failure and size reduction are realized.

In addition, in the coil component 10A according to the presentembodiment, the level difference L2 is set to zero, so that the landpatterns P12 and P14 can be disposed in edge portions of the respectivemounting regions 31 and 32. This can enhance use efficiency of thecircuit substrate. For example, even when a shortest distance betweenthe edge of the circuit substrate and land pattern is limited, the coilcomponent 10A can be mounted nearest the edge of the circuit substrate.

The following describes a method of forming the terminal electrodes E11to E14 on the drum-shaped core 20A.

First, the drum-shaped core 20A having the shape as illustrated in FIG.1 is produced, and an electrode material in a liquid or paste form isprepared. As illustrated in FIG. 5, an electrode material M in a liquidor paste form is poured into a container 40 having an opened upperportion. Then, the convex portions protruding from the mounting surfacesSb of the flange portions 22A and 23A are dipped in the electrodematerial M to thereby form the terminal electrodes on each mountingsurface Sb. At this time, a dipping depth is controlled so as not tobring the concave portions of each mounting surface Sb into contact withthe electrode material M. That is, the dipping depth is controlled suchthat a liquid surface of the electrode material M is positioned betweenthe convex and concave portions. A reference symbol B illustrated inFIG. 5 denotes a bottom surface of the concave portion. With thisprocedure, the four terminal electrodes E11 to E14 can be formed at thesame time on the mounting surfaces Sb of the flange portions 22A and 23Ain a single dipping process. That is, the terminal electrodes E11 to E14can be formed very easily by the dipping method without using a screenprinting method or a mask sputtering method.

After formation of the terminal electrodes E11 to E14, the wires W11 andW12 are wound around the winding core 21. Then, the end portions of thewires W11 and W12 are connected to the corresponding terminal electrodesE11 to E14, whereby the coil component 10A according to the presentembodiment is completed.

As described above, in the coil component 10A according to the presentembodiment, the mounting surface Sb of the drum-shaped core 20A has theconcavo-convex shape, so that the plurality of terminal electrodes E11to E14 can be formed easily by using the dipping method. The terminalelectrodes E11 to E14 are each formed on the top surface of thecorresponding convex portion and at the upper portions of the four sidesurfaces constituting the convex portion.

FIG. 6 is a schematic perspective view illustrating an externalappearance of a coil component 10A₁ according to a modification of thefirst embodiment.

The coil component 10A₁ according to the modification differs from theabove-described coil component 10A in that the level difference L2 isnot zero. Accordingly, in this modification, the level difference L1 isreduced by that much. That is, a value obtained by L1+L2 in thismodification is the same as that obtained in the first embodiment, andthus a relationship L1>L2 is satisfied. Other configurations are thesame as those of the first embodiment, so the same reference numeralsare used for the same elements, and repeated descriptions thereof areomitted here.

According to the present modification, when the coil components 10A₁ arearranged juxtaposed in the mounting regions 31 and 32 on the circuitsubstrate, respectively, an x-direction gap between the land patternsP11 and P12 (P13 and P14) of the different coil components 10A₁ isL0+L1+L2. This value is the same as that obtained by L0+L1 in the firstembodiment, so that it is possible to obtain the same effect as thatobtained by the coil component 10A according to the first embodiment.

As described above, although a difference between L1 and L2 is reducedin the present modification, the relationship L1>L2 is maintained. If L1is equal to L2, the land patterns P11 to P14 are largely separated fromthe edges of the mounting regions 31 and 32, with the result that theuse efficiency of the circuit substrate is deteriorated.

FIG. 7 is a schematic perspective view illustrating an externalappearance of a coil component 10B according to a second embodiment ofthe present invention.

A drum-shaped core 20B is used in the coil component 10B according tothe present embodiment. The drum-shaped core 20B has a pair of flangeportions 22B and 23B provided at y-direction both ends of the windingcore 21. The flange portions 22B and 23B each have three convexportions. As in the first embodiment, terminal electrodes are formedrespectively on top surfaces of the convex portions. Specifically, theflange portion 22B has three terminal electrodes E21 to E23, and theflange portion 23B has three terminal electrodes E24 to E26. Theplurality of terminal electrodes (e.g., E21 to E23) formed in the sameflange are electrically isolated from each other by the concave portion.

Four wires W21 to W24 are wound around the winding core 21. The wire W21is connected to the terminal electrodes E21 and E26, and a windingdirection thereof is, e.g., a clockwise direction. The wire W22 isconnected to the terminal electrodes E22 and E26, and a windingdirection thereof is, e.g., a counterclockwise direction. The wire W23is connected to the terminal electrodes E23 and E25, and a windingdirection thereof is, e.g., a clockwise direction. The wire W24 isconnected to the terminal electrodes E23 and E24, and a windingdirection thereof is, e.g., a counterclockwise direction.

With the above configuration, there is constructed a pulse transformerin which the terminal electrodes E21 and E22 are complementaryprimary-side terminals, the terminal electrodes E24 and E25 arecomplementary secondary-side terminals, the terminal electrode E26 is aprimary-side center tap, and the terminal electrode E23 is asecondary-side center tap.

In the present embodiment, an x-direction gap L12 between the terminalelectrodes E22 and E23 is larger than an x-direction gap L11 between theterminal electrodes E21 and E22 (L11>L12). Similarly, an x-direction gapL12 between the terminal electrodes E25 and E26 is larger than anx-direction gap L11 between the terminal electrodes E24 and E25(L11>L12). As a result, a breakdown voltage between the primary andsecondary sides is increased.

Out of the three convex portions formed on the flange portion 22B, theconvex portion closest to a first side surface S1 has a third sidesurface S3 parallel to the first side surface S1 and positioned at thefirst side surface S1 side, and a level difference between the first andthird side surfaces S1 and S3 is L1. On the other hand, out of the threeconvex portions formed on the flange portion 22B, the convex portionclosest to a second side surface S2 has a fourth side surface S4 formingthe same plane with the second side surface S2, and a level differenceL2 between the second and fourth side surfaces S2 and S4 is zero(L1>L2).

The drum-shaped core 20B has a two-fold rotation-symmetrical shape.Thus, the flange portion 23B has the same configuration as that of theabove-described flange portion 22B.

The coil component 10B according to the present embodiment can be usedas a pulse transformer PT for the LAN connector circuit (100 BASE)illustrated in FIG. 3 and the LAN connector circuit (1000 BASE)illustrated in FIG. 4. Also in this embodiment, as illustrated in FIG.8, mounting regions 33 and 34 are in proximity when high densitymounting is applied. Land patterns P21 to P26 illustrated in FIG. 8 arepatterns to be connected to the terminal electrodes E21 to E26,respectively.

Also in the present embodiment, as in the first embodiment, the leveldifference L1 is formed in each of the flange portions 22B and 23B, sothat an x-direction gap between the land patterns P21 and P23 (P24 andP26) of the different coil components 10B is increased to a valueobtained by L0+L1. Thus, even when the gap L0 is very small, the landgap between the different coil components 10B can sufficiently beensured, thereby making it possible to prevent a short circuit failure.

FIG. 9 is a schematic perspective view illustrating an externalappearance of a coil component 10B₁ according to a first modification ofthe second embodiment.

The coil component 10B₁ according to the first modification differs fromthe above-described coil component 10B in that the level difference L1is zero and that the level difference L2 has a predetermined length.That is, values of the level differences L1 and L2 are replaced witheach other. Other configurations are the same as those of the coilcomponent 10B, so the same reference numerals are used for the sameelements, and repeated descriptions thereof are omitted here. Even withsuch a configuration, when the coil components 10B₁ are mounted inproximity on the circuit substrate, an x-direction gap between the landpatterns P21 and P23 (P24 and P26) of the different coil component 10B₁is increased to a value obtained by L0+L2, thereby making it possible toprevent a short circuit failure.

FIG. 10 is a schematic perspective view illustrating an externalappearance of a coil component 10B₂ according to a second modificationof the second embodiment.

The coil component 10B₂ according to the second modification differsfrom the above-described coil component 10B in that the level differenceL2 is not zero. Accordingly, in this modification, the level differenceL1 is reduced by that much. That is, a value obtained by L1+L2 is thesame as that obtained in the coil component 10B, and thus a relationshipL1>L2 is satisfied. Other configurations are the same as those of thecoil component 10B, so the same reference numerals are used for the sameelements, and repeated descriptions thereof are omitted here. Even withsuch a configuration, when the coil components 10B₂ are mounted inproximity on the circuit substrate, an x-direction gap between the landpatterns P21 and P23 (P24 and P26) of the different coil component 10B₂is increased to a value obtained by L0+L1+L2, thereby making it possibleto prevent a short circuit failure.

FIG. 11 is a schematic perspective view illustrating an externalappearance of a coil component 10B₃ according to a third modification ofthe second embodiment.

The coil component 10B₃ according to the third modification differs fromthe above-described coil component 10B₁ in that the level difference L1is not zero. Accordingly, in this modification, the level difference L2is reduced by that much. That is, a value obtained by L1+L2 is the sameas that obtained in the coil component 10B₁, and thus a relationshipL1<L2 is satisfied. Other configurations are the same as those of thecoil component 10B₁, so the same reference numerals are used for thesame elements, and repeated descriptions thereof are omitted here. Evenwith such a configuration, when the coil components 10B₃ are mounted inproximity on the circuit substrate, an x-direction gap between the landpatterns P21 and P23 (P24 and P26) of the different coil component 10B₃is increased to a value obtained by L0+L1+L2, thereby making it possibleto prevent a short circuit failure.

FIG. 12 is a schematic perspective view illustrating an externalappearance of a coil component 10C according to a third embodiment ofthe present invention.

A drum-shaped core 20C is used in the coil component 10C according tothe present embodiment. The drum-shaped core 20C has a pair of flangeportions 22C and 23C provided at y-direction both ends of the windingcore 21. The flange portions 22C and 23C each have four convex portions.As in the first embodiment, terminal electrodes are formed respectivelyon top surfaces of the convex portions. Specifically, the flange portion22C has four terminal electrodes E31 to E34, and the flange portion 23Chas four terminal electrodes E35 to E38. The plurality of terminalelectrodes (e.g., E31 to E34) formed in the same flange are electricallyisolated from each other by the concave portion.

Four wires W31 to W34 are wound around the winding core 21. The wire W31is connected to the terminal electrodes E31 and E38, and a windingdirection thereof is, e.g., a clockwise direction. The wire W32 isconnected to the terminal electrodes E32 and E37, and a windingdirection thereof is, e.g., a counterclockwise direction. The wire W33is connected to the terminal electrodes E33 and E36, and a windingdirection thereof is, e.g., a clockwise direction. The wire W34 isconnected to the terminal electrodes E34 and E35, and a windingdirection thereof is, e.g., a counterclockwise direction.

With the above configuration, there is constructed a pulse transformerin which the terminal electrodes E31 and E32 are complementaryprimary-side terminals, the terminal electrodes E35 and E36 arecomplementary secondary-side terminals, the terminal electrodes E37 andE38 constitute a primary-side center tap, and the terminal electrodesE33 and E34 constitute a secondary-side center tap. The above pulsetransformer can be used as a pulse transformer PT for the LAN connectorcircuit (100 BASE) illustrated in FIG. 3 and the LAN connector circuit(1000 BASE) illustrated in FIG. 4.

In the present embodiment, an x-direction gap L22 between the terminalelectrodes E32 and E33 is larger than an x-direction gap L21 between theterminal electrodes E31 and E32 and an x-direction gap L23 between theterminal electrodes E33 and E34 (L21=L23<L22). Similarly, an x-directiongap L22 between the terminal electrodes E36 and E37 is larger than anx-direction gap L21 between the terminal electrodes E35 and E36 and anx-direction gap L23 between the terminal electrodes E37 and E38(L21=L23<L22). As a result, a breakdown voltage between the primary andsecondary sides is increased.

Out of the four convex portions formed on the flange portion 22C, theconvex portion closest to a first side surface S1 has a third sidesurface S3 parallel to the first side surface S1 and positioned at thefirst side surface S1 side, and a level difference between the first andthird side surfaces S1 and S3 is L1. On the other hand, out of the fourconvex portions formed on the flange portion 22C, the convex portionclosest to a second side surface S2 has a fourth side surface S4 formingthe same plane with the second side surface S2, and a level differenceL2 between the second and fourth side surfaces S2 and S4 is zero(L1>L2).

The drum-shaped core 20C has a two-fold rotation-symmetrical shape.Thus, the flange portion 23C has the same configuration as that of theabove-described flange portion 22C.

The coil component 10C according to the present embodimentshort-circuits the terminal electrodes E37 and E38 constituting theprimary-side center tap and short-circuits the terminal electrodes E33and E34 constituting the secondary-side center tap, thereby making itpossible for the coil component 10C to perform exactly the same functionas that of the coil component 10B according to the second embodiment.The short circuit of the center tap can be made on the circuitsubstrate. That is, the circuit substrate having a land patternillustrated in FIG. 13 is used, and the coil component 10C is mounted ina mounting region 35 on the circuit substrate, whereby the terminalelectrodes E33 and E34 can be short-circuited by a common land patternP33, and the terminal electrodes E37 and E38 can be short-circuited by acommon land pattern P36.

The land patterns P33 and P36 each have an x-direction width larger thanthose of the other land patterns P31, P32, P34, and P35. Thisfacilitates connection between the land pattern P33 and two terminalelectrodes E33 and E34 to be short-circuited and connection between theland pattern P36 and two terminal electrodes E37 and E38 to beshort-circuited. In FIG. 13, dashed lines E33, E34, E37, and E38indicate mounting positions of the respective terminal electrodes E33,E34, E37, and E38, and it can be seen that apart of the terminalelectrode and a part of the corresponding land pattern are overlappedwith each other in a plan view.

However, enlarging of the x-direction widths of the land patterns P33and P36 is not essential, but the land patterns P33 and P36 may eachhave the same x-direction width as those of the other land patterns P31,P32, P34, and P35, as illustrated in FIG. 14. Even in this case, theland pattern P33 needs to be overlapped with a part of each of theterminal electrodes E33 and E34 and to cover the entire area of a gapbetween the terminal electrodes E33 and E34. Similarly, the land patternP36 needs to be overlapped with a part of each of the terminalelectrodes E37 and E38 and to cover the entire area of a gap between theterminal electrodes E37 and E38.

In the above example, the terminal electrodes E33 and E34 areshort-circuited to be used as the secondary-side center tap, and theterminal electrodes E37 and E38 are short-circuited to be used as theprimary-side center tap; however, a configuration may be adopted inwhich the terminal electrodes E31 and E32 are short-circuited to be usedas the secondary-side center tap, and the terminal electrodes E35 andE36 are short-circuited to be used as the primary-side center tap. Inthis case, the terminal electrodes E33 and E34 are complementaryprimary-side terminals, and the terminal electrodes E37 and E38 arecomplementary secondary-side terminals.

FIG. 15 is a side view of the coil component 10C mounted on the circuitsubstrate.

In the example of FIG. 15, the terminal electrode E31 and the landpattern P31 are connected by a solder 51, the terminal electrode E32 andthe land pattern P32 are connected by a solder 52, and the terminalelectrodes E33, E34 and the land pattern P33 are connected by a solder53. The land patterns P31 and P32 have an x-direction size larger thanthose of the corresponding terminal electrodes E31 and E32, and a partof each of the terminal electrodes E31 and E32 is formed also on sidesurfaces of each of corresponding convex portion, so that the solders 51and 52 each form a fillet extending in the x-direction. Forming thesolder fillet increases bonding strength, thereby increasing reliabilityof a product after mounting.

On the other hand, the land pattern P33 is disposed so as to cover theentire area of a gap between the terminal electrodes E33 and E34, and apart of each of the terminal electrodes E33 and E34 is formed also onside surfaces of each of corresponding convex portion, so that thefillet of the solder 53 forms a bridge directly connecting the terminalelectrodes E33 and E34. As a result, the terminal electrodes E33 and E34are short-circuited not only via the land pattern P33 but also via thebridge of the solder 53. This realizes the short circuit more reliably.

Assuming that a gap (strictly speaking, a gap measured at anintermediate position in a height direction of the convex portion)between the convex portion corresponding to the terminal electrode E33and the convex portion corresponding to the terminal electrode E34 is a,and a height of each of the terminal electrodes E33 and E34 formed onthe side surfaces of each convex portion is b,

-   -   b/a≧⅓ is preferably satisfied, and    -   b/a≧½ is more preferably satisfied.        Satisfying this condition facilitates formation of the bridge of        the solder 53.

In order to form the bridge of the solder 53 more reliably, anx-direction gap between the terminal electrodes E33 and E34 may bereduced, as illustrated in FIG. 16. Specifically, assuming that anx-direction gap between the terminal electrodes E31 and E32 is L21 andthat an x-direction gap between the terminal electrodes E33 and E34 isL23, a relationship L21>L23 may be satisfied. Satisfying thisrelationship allows a distance between the opposing side surfaces of theconvex portion corresponding to the terminal electrode E33 and theconvex portion corresponding to the terminal electrode E34 to bereduced, so that it is possible to form the bridge reliably with asmaller amount of solder.

As illustrated in FIG. 17, the common land pattern P33 may have anx-direction width that covers completely the terminal electrodes E33 andE34. In this case, a fillet that extends outside is formed also in thesolder 53, so that it is possible to increase reliability of a productafter mounting.

It is apparent that the present invention is not limited to the aboveembodiments, but may be modified and changed without departing from thescope and spirit of the invention.

What is claimed is:
 1. A coil component comprising: a drum-shaped corehaving a pair of flange portions and a winding core positioned betweenthe pair of flange portions; a plurality of terminal electrodes formedon each of the flange portions; and a plurality of wires wound aroundthe winding core and connected to the terminal electrodes, wherein eachof the flange portions includes: a mounting surface substantiallyparallel to an axial direction of the winding core; and first and secondside surfaces substantially parallel to the axial direction of thewinding core and substantially parallel to each other, the mountingsurface has a plurality of convex portions and at least one concaveportion positioned between the plurality of convex portions, each of theterminal electrodes is formed at least on an associated one of theconvex portions such that the terminal electrodes are isolated by theconcave portion, the plurality of convex portions includes a firstconvex portion closest to the first side surface, the first convexportion having a third side surface that is substantially parallel tothe first side surface, the plurality of convex portions includes asecond convex portion closest to the second side surface, the secondconvex portion having a fourth side surface that is substantiallyparallel to the second side surface, and a level difference between thefirst side surface and the third side surface is larger than a leveldifference between the second side surface and the fourth side surface.2. The coil component as claimed in claim 1, wherein the terminalelectrodes are further formed on the third and fourth side surfaces. 3.The coil component as claimed in claim 1, wherein the second sidesurface and the fourth side surface form substantially the same plane.4. The coil component as claimed in claim 1, wherein the plurality ofconvex portions further includes third and fourth convex portions, thefirst, third, fourth, and second convex portions are arranged in thisorder, and the plurality of terminal electrodes include first, second,third, and fourth electrodes formed respectively on the first, second,third, and fourth convex portions.
 5. The coil component as claimed inclaim 4, wherein a gap between the third and fourth convex portions islarger than a gap between the first and third convex portions and a gapbetween the second and four convex portions.
 6. The coil component asclaimed in claim 5, wherein the gap between the first and third convexportions and the gap between the second and fourth convex portionsdiffer from each other.
 7. The coil component as claimed in claim 4,wherein the first, second, third, and fourth terminal electrodes areformed on side surfaces of the first, second, third, and fourth convexportions, respectively, when the gap between the first and third convexportions or the gap between the second and fourth convex portions is a,and a height of each of the first, second, third, and fourth terminalelectrodes formed on the side surfaces of the first, second, third, andfourth convex portions, respectively, is b, b/a≧⅓ is satisfied.
 8. Thecoil component as claimed in claim 1, wherein the drum-shaped core has atwo-fold rotation-symmetrical shape.
 9. A circuit substrate comprising:a substrate having a plurality of land patterns; and a coil componentmounted on the substrate, wherein the coil component includes: adrum-shaped core having a pair of flange portions and a winding corepositioned between the pair of flange portions; a plurality of terminalelectrodes formed on each of the flange portions; and a plurality ofwires wound around the winding core and connected to the terminalelectrodes, each of the flange portions includes: a mounting surfacesubstantially parallel to an axial direction of the winding core; andfirst and second side surfaces substantially parallel to the axialdirection of the winding core and substantially parallel to each other,the mounting surface has a plurality of convex portions and at least oneconcave portion positioned between the plurality of convex portions,each of the terminal electrodes is formed at least on an associated oneof the convex portions such that the terminal electrodes are isolated bythe concave portion, the plurality of convex portions includes a firstconvex portion closest to the first side surface, the first convexportion having a third side surface that is substantially parallel tothe first side surface, the plurality of convex portions includes asecond convex portion closest to the second side surface, the secondconvex portion having a fourth side surface that is substantiallyparallel to the second side surface, a level difference between thefirst side surface and the third side surface is larger than a leveldifference between the second side surface and the fourth side surface,and the circuit substrate further comprises a solder connecting theplurality of land patterns to the plurality of terminal electrodes. 10.The circuit substrate as claimed in claim 9, wherein at least two coilcomponents are mounted on the substrate such that the first side surfaceof one coil component and the second side surface of the other coilcomponent face each other.
 11. A circuit substrate comprising: asubstrate having a plurality of land patterns; and a coil componentmounted on the substrate, wherein the coil component includes: adrum-shaped core having a pair of flange portions and a winding corepositioned between the pair of flange portions; a plurality of terminalelectrodes formed on each of the flange portions; and a plurality ofwires wound around the winding core and connected to the terminalelectrodes, each of the flange portions includes: a mounting surfacesubstantially parallel to an axial direction of the winding core; andfirst and second side surfaces substantially parallel to the axialdirection of the winding core and substantially parallel to each other,the mounting surface has a plurality of convex portions and at least oneconcave portion positioned between the plurality of convex portions,each of the terminal electrodes is formed at least on an associated oneof the convex portions such that the terminal electrodes are isolated bythe concave portion, the plurality of convex portions includes a firstconvex portion closest to the first side surface, the first convexportion having a third side surface that is substantially parallel tothe first side surface, the plurality of convex portions includes asecond convex portion closest to the second side surface, the secondconvex portion having a fourth side surface that is substantiallyparallel to the second side surface, a level difference between thefirst side surface and the third side surface is larger than a leveldifference between the second side surface and the fourth side surface,the plurality of convex portions further includes third and fourthconvex portions, the first, third, fourth, and second convex portionsare arranged in this order, the plurality of terminal electrodes includefirst, second, third, and fourth electrodes formed respectively on thefirst, second, third, and fourth convex portions, the circuit substratefurther comprises a solder connecting the plurality of land patterns tothe plurality of terminal electrodes, and the plurality of land patternsincludes a first land pattern connected to the first terminal electrode,a second land pattern connected to the third terminal electrode, and athird land pattern connected in common to the second and fourth terminalelectrodes.
 12. The circuit substrate as claimed in claim 11, whereinthe second and fourth terminal electrodes are short-circuited via abridge of the solder.
 13. A method for manufacturing a coil component,the method comprising: preparing a drum-shaped core having a pair offlange portions and a winding core positioned between the pair of flangeportions; forming a plurality of terminal electrodes on each of theflange portions; and winding a plurality of wires around the windingcore and connecting end portions of the wire to the terminal electrodes,wherein each of the flange portions includes: a mounting surfacesubstantially parallel to an axial direction of the winding core; andfirst and second side surfaces substantially parallel to the axialdirection of the winding core and substantially parallel to each other,the mounting surface has a plurality of convex portions and at least oneconcave portion positioned between the plurality of convex portions,each of the terminal electrodes is formed at least on an associated oneof the convex portions such that the terminal electrodes are isolated bythe concave portion, the plurality of convex portions includes a firstconvex portion closest to the first side surface, the first convexportion having a third side surface that is substantially parallel tothe first side surface, the plurality of convex portions includes asecond convex portion closest to the second side surface, the secondconvex portion having a fourth side surface that is substantiallyparallel to the second side surface, a level difference between thefirst side surface and the third side surface is larger than a leveldifference between the second side surface and the fourth side surface,and the forming is performed by preparing an electrode material in aliquid or paste form and dipping the convex portions in the electrodematerial such that the concave portions is not brought into contact withthe electrode material.